Gabo Island is the granite island off Cape Howe at the very eastern end of Victoria, 14 km from Mallacoota, crowned by the 47 m pink-granite lighthouse of 1862 – the second tallest in Australia – and home to one of the largest little penguin colonies in the world. It is the only offshore island in East Gippsland that a diver can reasonably reach, via the Mallacoota charter boats that run lighthouse and wildlife trips, and Santa Barbara Bay on its north-western side – the island's only sandy beach, with a jetty – is described by Visit Mallacoota as the best shallow spot, suitable for all skill levels. The bay is a natural harbour of granite arms enclosing sand and seagrass, and the diving is along those arms: boulders and ledges under bull kelp and mixed algae in 3–20 m, with sponge, ascidian and bryozoan patches in the shade, abalone and sea urchins on every surface (this is abalone country), crayfish in the ledges and a fish community that marks the meeting of Victorian and NSW faunas – banded morwong, blue groper, wrasses of several species, sweep, luderick, drummer, leatherjackets and, in warm summers, tropical strays carried down on the East Australian Current.

Dolphins and stingrays are regulars at the jetty, fur seals haul out near it, and the penguins come and go at dawn and dusk. The island's outer coasts, facing the Tasman, are steep granite dropping to deeper water with richer sponge cover, and the wreck of the SS Monumental City (1853) lies off Tullaberga Island to the west; both are calm-day, experienced-diver propositions. East of the island the Cape Howe Marine National Park is no-take; Gabo itself is outside it.

Everything about Gabo is self-organised – the charters carry divers but do not guide, there is no air in Mallacoota, and the weather decides the day – but the reward is a clear-water granite island with a lighthouse, penguins, seals and warm-temperate fish that almost no Victorian divers have visited. Lighthouse-keeper's cottage accommodation is bookable through Parks Victoria for those who want to stay and snorkel the bay at leisure.

Boat or air only. Charter boats from Mallacoota – Mallacoota Fishing Charters and Tours, Wilderness Coast Charters (03 5158 0701) and Gabo Island Escapes – make the 14 km run in 30–45 minutes, weather permitting, landing at the Santa Barbara Bay jetty; they carry divers and gear by arrangement but do not guide dives. Private boats launch at the Bastion Point ocean ramp (swell-dependent) and cross the same water.

Merimbula Air Services flies visitors in for lighthouse stays, though not with dive gear. Santa Barbara Bay is the sheltered anchorage and dive area; the island's exposed southern and eastern sides face the Tasman Sea and are for calm days only. Parks Victoria manages the island and the lighthouse accommodation.

The crossing from Mallacoota and the island's exposed sides depend on swell: charters describe their services as weather dependent and advise flexibility, and easterly or southerly swell over 1.5 m stops them. Santa Barbara Bay faces north-west and is sheltered from the prevailing south-westerly and from Tasman swell, so it is diveable on most days that the boats run; the eastern and southern granite is for flat calms. Tidal flow is moderate around the island's points.

Late summer and autumn bring warm, clear East Australian Current water; whales pass May–November; penguins return to the colony at dusk year-round.

From the boat or beach in Santa Barbara Bay, descend beside the jetty and work out along the granite on either side of the bay at 5–12 m, keeping the rock on one shoulder, through the kelp and boulders where the blue groper and banded morwong live; extend to 15–20 m at the bay's mouth in calm conditions. Turn at half gas, return along the same rocks and finish at the jetty, watching for the resident rays and dolphins.

No dive operator. Mallacoota Fishing Charters and Tours, Wilderness Coast Charters and Gabo Island Escapes provide boat transport to the island (weather dependent) and will carry divers by arrangement; diving is self-guided. No air in Mallacoota.